1. Field of the Invention
The present invention relates to a carrier and a two-component developer containing such a carrier.
2. Description of the Related Art
Conventionally, various carriers, which include a coat-type carrier made by coating magnetic particles with a resin, a binder-type carrier made by dispersing magnetic particles in a binder resin and a carrier using magnetic particles as they are, have been known. However, the application of any of these types of carriers causes the toner component to adhere to the carrier surface (to be spent), when used for a long time, resulting in a reduction in the chargeable points and the subsequent failure in maintaining the initial charge-applying capability of the carrier. The reduction in the initial charge-applying capability causes a failure in obtaining a predetermined quantity of charge, resulting in fog on a copied image.
Moreover, in the case when the coat-type carrier and the binder-type carrier having a resin on the surface thereof are used to copy an image having continuous areas with a comparatively high density and a comparatively low density for a long time, a problem (referred to as a lead-off phenomenon) arises, in which an image-less portion occurs in the border between the high-density area and the low-density area on the copied image.
Furthermore, the application of the carrier of the type using magnetic particles as they are causes a problem in which the carrier is developed together with the toner and spent at the time of continuous copying processes.
Here, in order to improve the binding properties of the coating material, with respect to the coat-type carrier, a carrier has been proposed in which a porous spherical carrier base material, made by sintering magnetic particles, is coated with a resin (Japanese Patent Laid-Open No. Hei. 8-160673). Such sintered spherical magnetic particles used as the carrier base material are obtained by highly filling the resin with magnetic particles, forming this into a spherical shape, and sintering the resulting particle. However, in the carrier of this type also, the problems of fog (due to separation of the coating material) and lead-off have still arisen during endurance copying processes.